Gas gauge quit working

[j7l2]

2002 Chev sub with 8100, 4l80e trans. Gauge goes to full when tank is filled. Will drop about normal to 3/4 while driving, then it stops. It won't move again until you have approx 6 gal of gas left . Then goes to 1/2 tank. Dealer has replaced sending units in the tank, has verified that gauge works with OBDII, and relaced PCM. End result: No change. Any ideas? It is still under warrenty, but what do you replace next?
Thanks for any ideas and comments.
Regards,
JimO

[madmatt]

The IPC is the only other part to replace. Just because the needle sweeps on command w/ Tech 2 doesn't mean it's calibrated right. your dealer should have a tool that can be hooked to the harness that goes to the fuel level sender and vary the level of resistence in the circuit. there are specs for different levels of fuel. monitering the fuel level parameter w/ tech 2 and watching the gauge in the IPC simply see where the problem is. PCM reads right, replace the IPC. both read wrong, use a ohm meter to verify the tool resistence is right and recheck. both read wrong again, replace the PCM. Broken down, diagnoising is so simple yet many techs and sometimes entire shops don't take the time to do it right and take the shotgun approach and shoot parts at it.

[ 03-06-2005, 05:49 PM: Message edited by: madmatt ]

[j7l2]

Madmatt,
Thank you for the suggestions. I talked to the dealer and they checked the IPC the way you said. It checks okay. They are a loss as to what is causing the gauge to read incorrectly. They are going to see if GM Tech as any ideas.

Thanks again,
JimO

[madmatt]

Got me stumped then. I'd say that GM TAC probably won't have a clue and will have them replace the IPC since it's not been. The problem w/ TAC is that sometimes you'll get someone who really knows their sh!t but most of the time you get a complete retard who knows only what they read on their PC screen a do nothing but give techs the run around and waste our time telling us which parts to throw at it next when we could have figured that out on our own....sorry just venting,,,,,TAC really gets me going. I always get the morons!

[MIKE MOG]

I KNOW WHAT YOUR TALKING ABOUT MADMATT! ALONG WITH ALL OF THE CASE#'S FROM US AND THE I USED TO BE A TECH ALSO, I DON;T THINK SOME OF THOSE GUYS HAVE A CLUE.
MIKE

[madmatt]

For real!!!! I think some of those guys got put there out of pity and the fact they couldn't fix a ball point ink pen..... I worked on a 04 Z06 for 8 hrs just trying to figure out where the noise in the rear end was coming from. My FORTH call to TAC got me the INTERNAL PI BS!! It blew me away when three other consultants couldn't find this and tell me all I needed to do was flush the GETRAG diff and fill w/ lube + the additive. and what good does a internal pi do us, they won't even fax me a copy of one when I need it. I was trying to get a D-max running right one day, called TAC hoping for some quick help(don't know what I was thinking) and the dude actually asked me what the lift pump press. was!!!!!!!

[j7l2]

An update: Yesterday the dealer replaced the IPC in my truck and guess what No difference! They then called GM Tech and discussed the problem again. Now they are being told it is a bad ground circuit between gas gauge and PCM. Supposedly there is a spliced ground in the wiring that has given GM problems. So its back in the shop next Thursday/Friday so the dealer can check out the wiring. Anyone aware of this ground problem?
Thanks for your input,
JimO

[madmatt]

haven't heard of it.

[markrinker]

My fuel guage ('03 K3500) is showing signs of inaccuracy as well. Today dropped from 1/4 to E but the odometer told me I had at least 8 gallons left.

Drove about 40, stopped for fuel, put in 28 of 32 gallon capacity. This time the guage went to about 7/8 tank, but was absolutely full.

Let me know what you find out. I don't really need a fuel gauge as I monitor the trip OD on each haul, but it would be nice to have it work properly, or not work at all...anything in between is a pain.

Also, its doesn't matter much when you stop at EVERY gas station like I do...lol

[j7l2]

Finally fixed!
GM sent a factory rep to my dealer. He along with the mechanic went over the entire fuel gage system. His conclusion was that something was wrong with the new sending unit that the dealer installed. So they dropped the tanks and removed the sending unit. They immediately saw the problem. The wiring (from the sending unit) that is in the tank had become intangled in the float arm and not allow it full movement. They ordered and installed another new sending unit using a wire tie to limit slack in the wiring. Now the gage works fine. This had to cost GM alot. I am very pleased with both my Dealers support and GM's persistance in fixing my problem.
Thanks to everyone on TDP for their interest and input.
Regards,
JimO

[madmatt]

sweet! glad to hear you finally got'er fixed!